The volatility of fuel (e.g., the Reid Vapor Pressure (RVP)) is an essential parameter for the proper functioning of an internal combustion engine. In addition, it is important to know the value of this parameter to perform accurate leak detection.
International patent application publication no. WO2007071659, entitled “Method for the onboard determination of the volatility of a fuel”, in the name of the present applicant, discloses a method for the onboard determination of the volatility of a fuel stored in a fuel tank, which is part of a fuel system controlled by a fuel system control unit (FSCU) and comprising pressure, temperature and fuel level sensors, according to which the FSCU uses the ideal gas law and measurements performed by the sensors in order to predict the distillation curve and/or the Driveability Index (DI) of the fuel. The method is used to adjust the amount of fuel to be injected in a mixing chamber of an internal combustion engine of a motor vehicle.
Another known device, disclosed in US 2010/0332108 A1, relies on a combination of pressure variation and temperature variation to produce an estimate of the Reid Vapor Pressure (RVP).
It is a disadvantage of the known methods and devices, that they require sufficiently different thermodynamic states of the system, in terms of temperature and pressure, to allow the calculation of the volatility of the fuel from the ideal gas law. As the temperature of the system evolves slowly, this implies that a relatively long time elapses before the determination of the volatility of the fuel can be completed.